The present invention relates to an apparatus for driving a compressor and a refrigerating air conditioner, and is specifically suited to an apparatus for driving a compressor used in vapor compression refrigerating cycle, and a refrigerating air conditioner, such as air conditioners, refrigerators, cold storages, or the like, on which the apparatus is mounted.
As an apparatus for driving a compressor according to prior art 1, there is one disclosed in JP-A-5-211796. With the compressor, DC voltage is obtained by supplying an AC power source to a converter, three-phase AC voltage is obtained by supplying the DC voltage to an inverter, and the three-phase AC voltage is further supplied to an armature winding of a brushless DC motor. Further, with the compressor, an induced voltage detection unit is used to detect an induced voltage of the brushless DC motor to indirectly detect pole positions, and an operating frequency command value and a detection signal from the induced voltage detection unit are input, and an inverter control unit supplies to the inverter an inverter control signal for carrying out current control or voltage control, speed control, or the like. In addition, the brushless DC motor comprises a permanent magnet provided on a rotor core.
As an air conditioner according to prior art 2, there is one disclosed in JP-A-2001-3864. The air conditioner includes a refrigerating cycle, in which a compressor, a condenser, a restrictor, and an evaporator are connected together by means of a refrigerant piping, and comprises a permanent-magnet built-in induction motor, which starts as an induction motor at the start of driving the compressor, and causes synchronous pull-in near the number of synchronous revolutions to perform synchronous operation, bidirectional switching elements provided on respective phases of a three-phase circuit, which connects between the permanent-magnet built-in induction motor and three-phase power source for supplying electricity to the permanent-magnet built-in induction motor, and control means for causing intermittent conduction of the switching elements at 1/(6n+1) times a frequency of a commercial electric source (n is a positive integer).
As a permanent-magnet electric motor according to prior art 3, there is one disclosed in JP-A-9-322444. The permanent-magnet electric motor comprises a permanent magnet and a cage conductor, which are provided on a rotor, and an inverter device provided integral with a motor body can control operation of the motor. The prior art 3 describes that since the cage conductor is provided on the rotor, the motor can be started and operated as an induction motor when directly operated by a commercial electric source in the case where the inverter device gets out of order.
The prior art 1 involves a problem that while the use of the brushless DC motor makes the apparatus highly efficient as compared with three-phase induction motors, in order to start and drive the brushless DC motor, it is necessary to detect an induced voltage of the brushless DC motor to indirectly detect pole positions to control the inverter device, which leads to complexity in control of the inverter device to make the apparatus expensive. Also, the prior art 1 involves a further problem that since the AC power source supplies electricity to the brushless DC motor simply via the inverter device, operation of the brushless DC motor cannot be continued in the case where the inverter device gets out of order.
Also, the prior art 2 involves a problem that fine control is difficult since the control means simply controls the bidirectional switching elements provided on the respective phases so as to cause intermittent conduction. Also, the prior art 2 involves a further problem that since the AC power source simply supplies electricity to the permanent-magnet built-in induction motor via the bidirectional switching elements, operation of the permanent-magnet built-in induction motor cannot be continued in the case where the bidirectional switching elements get out of order.
Also, the prior art 3 relates to an electric motor but discloses nothing with respect to an apparatus for driving a compressor, and a refrigerating air conditioner. Also, with the prior art 3, in the case where the inverter device gets out of order, it becomes necessary to dismount the inverter device to reconnect directly to a commercial electric source, which is estimated to involve a very troublesome work.
It is an object of the invention to obtain an apparatus for driving a compressor and a refrigerating air conditioner, which use an inexpensive inverter control to be favorable in starting quality and capable of highly efficient operation.
It is another object of the invention to obtain an apparatus for driving a compressor and a refrigerating air conditioner, in which an inexpensive inverter control is used to enable an operation, which is favorable in starting quality and highly efficient, and which can be readily operated with a commercial electric source even when an inverter device gets out of order, and are highly reliable.
Other objects and advantages of the invention will be made apparent from the following description.